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Teton Dam
Teton Dam
The reservoir behind the Teton Dam was emptied within hours of the initial breach
Official name Teton Dam
Impounds Teton River
Locale Fremont / Madison counties, Idaho
Length 3,100 feet (940 m)
Height 305 feet (93 m)
Width (at base) 1,700 feet (520 m)
Construction began 1975
Opening date 1976
Construction cost $48,825,000
Reservoir information
Creates Teton Reservoir
Capacity 234,259 acre feet (288,954,000 m3)
Maintained by United States Bureau of Reclamation

The Teton Dam was a federally built earthen dam on the Teton River in southeastern Idaho, set between Fremont and Madison Counties, USA which when filling for the first time suffered a catastrophic failure on June 5, 1976. The collapse of the dam resulted in the deaths of 11 people[1] and 13,000 head of cattle. The dam cost about USD $100 million to build, and the federal government paid over $300 million in claims related to the dam failure. Total damage estimates have ranged up to $2 billion.[2] The dam was never rebuilt.

Contents

Geology

The ruins of the Teton Dam.

The dam site is located in the eastern Snake River Plain, which is a broad tectonic depression on top of rhyolitic ash-flow tuff. The tuff, a late-Cenozoic volcanic rock dating to about 1.9 million years, sits on top of sedimentary rock. The area is very permeable, highly fissured and unstable. Test boreholes, drilled by engineers and geologists employed by the Bureau of Reclamation, U.S. Department of the Interior, showed that one side of the canyon was highly fissured, a condition unlikely to be remediated by the Bureau's favoured method of "grouting" (injecting concrete into the substrates under high pressure).

No seepage was noted on the dam itself before the date of the collapse. However, on June 3, 1976 workers found two small springs had opened up downstream.

The collapse and flood

At the time of the collapse, spring runoff had almost filled the new reservoir to capacity, with a maximum depth of 240 feet (73 m). Water began seeping from the dam on the Thursday before the collapse, an event not unexpected for an earthen dam. The only structure that had been initially prepared for releasing water were the emergency outlet works, which could carry just 850 cubic feet per second (24 m3/s). Although the reservoir was still rising over 4 feet (1.2 m) per day, the main outlet works and spillway gates were not yet in service. The spillway gates were cordoned off by steel walls while they were being painted.

On Saturday, June 5, 1976, at 7:30 a.m., a muddy leak appeared, suggesting sediment was in the water, but engineers did not believe there was a problem. By 9:30 a.m. the downstream face of the dam had developed a wet spot erupting water at 20 to 30 cubic feet per second (0.57 to 0.85 m3/s) and embankment material began to wash out. Crews with bulldozers were sent to plug the leak, but were unsuccessful. Local media appeared at the site, and at 11:15 officials told the county sheriff's office to evacuate downstream residents. Work crews were forced to flee on foot as the widening gap, now over the size of a swimming pool, swallowed their equipment. The operators of two bulldozers caught in the eroding embankment were pulled to safety with ropes.

At 11:55 a.m. Mountain Daylight Time (UTC-6:00), the crest of the dam sagged and collapsed into the reservoir; two minutes later the remainder of the right-bank third of the main dam wall disintegrated. Over 2,000,000 cubic feet per second (57,000 m3/s) of sediment filled water emptied through the breach into the remaining 6 miles (9.7 km) of the Teton River canyon, after which the flood spread out and shallowed on the Snake River Plain. By 8:00 p.m. that evening, the reservoir had completely emptied, although over two-thirds of the dam wall remained standing.

Cause of the collapse

Study of the dam's environment and structure[3] placed blame on the collapse on the permeable Loess soil used in the core and on fissured (cracked) Rhyolite in the foundations of the dam that allowed water to seep under the dam. The permeable Loess was found to be cracked. It is postulated that the combination of these flaws allowed water to seep through the dam and led to internal erosion, called piping, that eventually caused the dam's collapse.

A wide-ranging controversy erupted from the dam's collapse. According to the Bureau of Reclamation,

Today, Bureau of Reclamation engineers assess all Reclamation dams under strict criteria established by the Safety of Dams program. Each structure is periodically reviewed for resistance to seismic stability, internal faults and physical deterioration.[4]

Deaths, damage and property claims

Teton Canyon comes to an end approximately six miles below the dam site, at this point the river flows into the Snake River Plain. When the dam failed, the freed waters struck several communities immediately downstream, particularly Wilford at the terminus of the canyon, Sugar City, Salem, Hibbard and Rexburg. Thousands of homes and businesses were destroyed. The small agricultural communities of Wilford and Sugar City were literally wiped from the river bank. Five of the eleven deaths attributed to the flood occurred in Wilford. The similar community of Teton City, on the south bank of the river, is sited on a modest elevation and was largely spared.[2] One Teton resident was fishing on the river at the time of the dam failure and was drowned. An elderly woman living in Teton City died as a result of the evacuation. {"Teton Dam Flood, June 5, 1976", by Elaine Johnson, http://www.rootsweb.ancestry.com/~idfremon/flood.htm}

One estimate placed damage to Hibbard and Rexburg area, with a population of approximately 10,000, at 80 percent of existing structures. The Snake River flows through the industrial, commercial and residential districts of north Rexburg. A significant reason for the massive damage in the community was the location of a large commercial lumber yard directly upstream. When the flood waters hit, thousands of board feet of timber snapped from their moorings, caught fire from leaking gas, and were swept downstream. The force of the logs and cut lumber, and the subsequent fires, practically destroyed the city.

The flood waters traveled west along the route of the south fork of the Snake, around the Menan Buttes, significantly damaging the community of Roberts. The city of Idaho Falls, even further down on the flood plain, had time to prepare. At the older American Falls Dam downstream, engineers increased discharge by less than 5% before the flood arrived.[5] That dam held, and the flood was effectively over, but tens of thousands of acres of land near the river were stripped of fertile topsoil.[2]

The force of the Teton dam failure destroyed the lower part of the Teton River, washing away riparian zones and reducing the canyon walls. This seriously damaged the stream ecology, and the native cutthroat trout population has been endangered. The force of the water and excessive sediment also damaged stream habitat in the Snake River and some tributaries, at least as far downstream as Fort Hall, Idaho.

After the dam's collapse, debris clean up began immediately and took the rest of the summer. Rebuilding of damaged property continued for several years. Within a week after the disaster, President Gerald Ford requested a $200 million appropriation for initial payments for damages, without assigning responsibility for Teton Dam’s failure.

The Bureau of Reclamation set up claims offices in Rexburg, Idaho Falls, and Blackfoot. By January 4, 1977, disaster victims filed over 4,800 claims totalling $194 million. By that date, the Federal government paid 3,813 of those claims, $93.5 million. Originally scheduled to end in July 1978, the Claims Program continued into the 1980s. At the end of the Claims Program in January 1987, the Federal government had paid 7,563 claims for a total amount of $322 million.

Possible reconstruction

No plans were made for rebuilding the Teton Dam immediately after the disaster.[1] However, as of July 2009, there was new speculation about rebuilding in order to provide water for irrigation, one of the purposes of the original structure. The Bureau of Reclamation has reportedly set aside $400,000 of the $800,000 needed to study the feasibility of rebuilding. A local Idaho news station, "Local News Channel 8" ran a two part special on the process and reactions by local residents.

See also

References

External links

Coordinates: 43°54′35″N 111°32′21″W / 43.90972°N 111.53917°W / 43.90972; -111.53917

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Simple English

on June 5, 1976.]]

Teton Dam was a dam on the Teton River in Idaho, in the USA. When it was built, it was 3,100 feet (940 m) long and 305 feet (93 m) tall, making it one of the largest dams in the United States. It is most known for collapsing during spring runoff on June 5, 1976, and the resulting flood destroyed 10,000 acres of land and five cities.

The dam was never rebuilt. Although the U.S. Government paid $100 million to build the dam, it had to pay $300 million more dollars to pay for flood damages.



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